Gradient-Echo T2WI magnetic resonance imaging (MRI) is most sensitive method for diagnosing cavernous hemangiomas. MRI is such a powerful tool for diagnosis, it has led to an increase in diagnosis of cavernous hemangiomas since the technology's advent in the 1980s. The radiographic appearance is most commonly described as "popcorn" or "mulberry"-shaped. Computed tomography (CT) scanning is not a sensitive or specific method for diagnosing cavernous hemangiomas. Angiography is typically not necessary, unless it is required to rule out other diagnoses. Additionally, biopsies can be obtained from tumor tissue for examination under a microscope. It is essential to diagnose cavernous hemangioma because treatments for this benign tumor are less aggressive than that of cancerous tumors, such as angiosarcoma. However, since MRI appearance is practically pathognomonic, biopsy is rarely needed for verification.

In the treatment of a brain cavernous hemangioma, neurosurgery is usually the treatment chosen. Research needs to be conducted on the efficacy of treatment with stereotactic radiation therapy, especially on the long-term. However, radiotherapy is still being studied as a form of treatment if neurosurgery is too dangerous due the location of the cavernoma. Genetic researchers are still working on determining the cause of the illness and the mechanism behind blood vessel formation. Clinical trials are being conducted to better assess when it is appropriate to treat a patient with this malformation and with what treatment method. Additionally, long term studies are being conducted because there is no information related to the long-term outlook of patients with cavernoma. A registry exists known as The International Cavernous Angioma Patient Registry collects information from patients diagnosed with cavernoma in order to facilitate discovery of non-invasive treatments.

Both computed tomography angiography (CTA) and magnetic resonance angiography (MRA) have been proved to be effective in diagnosing intracranial vascular malformations after ICH. So frequently, a CT angiogram will be performed in order to exclude a secondary cause of hemorrhage or to detect a "spot sign".

Intraparenchymal hemorrhage can be recognized on CT scans because blood appears brighter than other tissue and is separated from the inner table of the skull by brain tissue. The tissue surrounding a bleed is often less dense than the rest of the brain because of edema, and therefore shows up darker on the CT scan.

When due to high blood pressure, they typically occur in the putamen or thalamus (60%), cerebrum (20%), cerebellum (13%) or pons (7%).

The original criteria for IIH were described by Dandy in 1937.

They were modified by Smith in 1985 to become the "modified Dandy criteria". Smith included the use of more advanced imaging: Dandy had required ventriculography, but Smith replaced this with computed tomography. In a 2001 paper, Digre and Corbett amended Dandy's criteria further. They added the requirement that the patient is awake and alert, as coma precludes adequate neurological assessment, and require exclusion of venous sinus thrombosis as an underlying cause. Furthermore, they added the requirement that no other cause for the raised ICP is found.

In a 2002 review, Friedman and Jacobson propose an alternative set of criteria, derived from Smith's. These require the absence of symptoms that could not be explained by a diagnosis of IIH, but do not require the actual presence of any symptoms (such as headache) attributable to IIH. These criteria also require that the lumbar puncture is performed with patient lying sideways, as a lumbar puncture performed in the upright sitting position can lead to artificially high pressure measurements. Friedman and Jacobson also do not insist on MR venography for every patient; rather, this is only required in atypical cases (see "diagnosis" above).

Diagnosis is principally by MRI. Frequently, arachnoid cysts are incidental findings on MRI scans performed for other clinical reasons. In practice, diagnosis of symptomatic arachnoid cysts requires symptoms to be present, and many with the disorder never develop symptoms.

Additional clinical assessment tools that can be useful in evaluating a patient with arachnoid cysts include the mini-mental state examination (MMSE), a brief questionnaire-based test used to assess cognition.

Neuroimaging, usually with computed tomography (CT/CAT) or magnetic resonance imaging (MRI), is used to exclude any mass lesions. In IIH these scans typically appear to be normal, although small or slit-like ventricles, dilatation and buckling of the optic nerve sheaths and "empty sella sign" (flattening of the pituitary gland due to increased pressure) and enlargement of Meckel's caves may be seen.

An MR venogram is also performed in most cases to exclude the possibility of venous sinus stenosis/obstruction or cerebral venous sinus thrombosis. A contrast-enhanced MRV (ATECO) scan has a high detection rate for abnormal transverse sinus stenoses. These stenoses can be more adequately identified and assessed with catheter cerebral venography and manometry. Buckling of the bilateral optic nerves with increased perineural fluid is also often noted on MRI imaging.

Lumbar puncture is performed to measure the opening pressure, as well as to obtain cerebrospinal fluid (CSF) to exclude alternative diagnoses. If the opening pressure is increased, CSF may be removed for transient relief (see below). The CSF is examined for abnormal cells, infections, antibody levels, the glucose level, and protein levels. By definition, all of these are within their normal limits in IIH. Occasionally, the CSF pressure measurement may be normal despite very suggestive symptoms. This may be attributable to the fact that CSF pressure may fluctuate over the course of the normal day. If the suspicion of problems remains high, it may be necessary to perform more long-term monitoring of the ICP by a pressure catheter.

CT scan (computed tomography) is the definitive tool for accurate diagnosis of an intracranial hemorrhage. In difficult cases, a 3T-MRI scan can also be used.

When ICP is increased the heart rate may be decreased.

It is important that a person receive medical assessment, including a complete neurological examination, after any head trauma. A CT scan or MRI scan will usually detect significant subdural hematomas.

Subdural hematomas occur most often around the tops and sides of the frontal and parietal lobes. They also occur in the posterior cranial fossa, and near the falx cerebri and tentorium cerebelli. Unlike epidural hematomas, which cannot expand past the sutures of the skull, subdural hematomas can expand along the inside of the skull, creating a concave shape that follows the curve of the brain, stopping only at the dural reflections like the tentorium cerebelli and falx cerebri.

On a CT scan, subdural hematomas are classically crescent-shaped, with a concave surface away from the skull. However, they can have a convex appearance, especially in the early stage of bleeding. This may cause difficulty in distinguishing between subdural and epidural hemorrhages. A more reliable indicator of subdural hemorrhage is its involvement of a larger portion of the cerebral hemisphere since it can cross suture lines, unlike an epidural hemorrhage. Subdural blood can also be seen as a layering density along the tentorium cerebelli. This can be a chronic, stable process, since the feeding system is low-pressure. In such cases, subtle signs of bleeding such as effacement of sulci or medial displacement of the junction between gray matter and white matter may be apparent. A chronic bleed can be the same density as brain tissue (called isodense to brain), meaning that it will show up on CT scan as the same shade as brain tissue, potentially obscuring the finding.

Diagnosis commonly occurs later in childhood and often occurs incidentally in asymptomatic patients or as a cause of visual impairment. The first symptoms are commonly found during routine vision screenings.

A number of examinations can be used to determine the extent of the syndrome and its severity. Fluorescein angiography is quite useful in diagnosing the disease, and the use of ultrasonography and optical coherence tomography (OCT) are helpful in confirming the disease. Neuro-ophthalmic examinations reveal pupillary defects (see Marcus Gunn Pupil). Funduscopic examinations, examinations of the fundus of the eye, allow detection of arteriovenous malformations. Neurological examinations can determine hemiparesis and paresthesias. Malformations in arteriovenous connections and irregular functions in the veins may be distinguished by fluorescein angiographies. Cerebral angiography examinations may expose AVMs in the cerebrum. MRIs are also used in imaging the brain and can allow visualization of the optic nerve and any possible atrophy. MRI, CT, and cerebral angiography are all useful for investigating the extent and location of any vascular lesions that are affecting the brain. This is helpful in determining the extent of the syndrome.

A "subarachnoid hemorrhage" is bleeding into the subarachnoid space—the area between the arachnoid membrane and the pia mater surrounding the brain. Besides from head injury, it may occur spontaneously, usually from a ruptured cerebral aneurysm. Symptoms of SAH include a severe headache with a rapid onset ("thunderclap headache"), vomiting, confusion or a lowered level of consciousness, and sometimes seizures. The diagnosis is generally confirmed with a CT scan of the head, or occasionally by lumbar puncture. Treatment is by prompt neurosurgery or radiologically guided interventions with medications and other treatments to help prevent recurrence of the bleeding and complications. Since the 1990s, many aneurysms are treated by a minimal invasive procedure called "coiling", which is carried out by instrumentation through large blood vessels. However, this procedure has higher recurrence rates than the more invasive craniotomy with clipping.

Imaging studies are performed before surgery or biopsy to preclude an intracranial connection. Images usually show a sharply circumscribed but expansile mass. It may be difficult to exclude the intracranial connection if the defect is small whether employing computed tomography or magnetic resonnance.

Treatment of a subdural hematoma depends on its size and rate of growth. Some small subdural hematomas can be managed by careful monitoring until the body heals itself. Other small subdural hematomas can be managed by inserting a temporary small catheter through a hole drilled through the skull and sucking out the hematoma; this procedure can be done at the bedside. Large or symptomatic hematomas require a craniotomy, the surgical opening of the skull. A surgeon then opens the dura, removes the blood clot with suction or irrigation, and identifies and controls sites of bleeding. Postoperative complications include increased intracranial pressure, brain edema, new or recurrent bleeding, infection, and seizure. The injured vessels must be repaired.

Depending on the size and deterioration, age of the patient, and anaesthetic risk posed, subdural hematomas occasionally require craniotomy for evacuation; most frequently, simple burr holes for drainage; often conservative treatment; and rarely, palliative treatment in patients of extreme age or with no chance of recovery.

In those with a chronic subdural hematoma, but without a history of seizures, the evidence is unclear if using anticonvulsants is harmful or beneficial.

There are various neuroimaging investigations that may detect cerebral sinus thrombosis. Cerebral edema and venous infarction may be apparent on any modality, but for the detection of the thrombus itself, the most commonly used tests are computed tomography (CT) and magnetic resonance imaging (MRI), both using various types of radiocontrast to perform a venogram and visualise the veins around the brain.

Computed tomography, with radiocontrast in the venous phase ("CT venography" or CTV), has a detection rate that in some regards exceeds that of MRI. The test involves injection into a vein (usually in the arm) of a radioopaque substance, and time is allowed for the bloodstream to carry it to the cerebral veins - at which point the scan is performed. It has a sensitivity of 75-100% (it detects 75-100% of all clots present), and a specificity of 81-100% (it would be incorrectly positive in 0-19%). In the first two weeks, the "empty delta sign" may be observed (in later stages, this sign may disappear).

Magnetic resonance venography employs the same principles, but uses MRI as a scanning modality. MRI has the advantage of being better at detecting damage to the brain itself as a result of the increased pressure on the obstructed veins, but it is not readily available in many hospitals and the interpretation may be difficult.

Cerebral angiography may demonstrate smaller clots than CT or MRI, and obstructed veins may give the "corkscrew appearance". This, however, requires puncture of the femoral artery with a sheath and advancing a thin tube through the blood vessels to the brain where radiocontrast is injected before X-ray images are obtained. It is therefore only performed if all other tests give unclear results or when other treatments may be administered during the same procedure.

Magnetic resonance imaging is less effective than CT at directly imaging sites of CSF leak. MRI studies may show pachymeningeal enhancement (when the dura mater looks thick and inflamed), sagging of the brain, pituitary enlargement, subdural hygromas, engorgement of cerebral venous sinuses, and other abnormalities. For 20% of patients, MRIs present as completely normal. There is disagreement over whether MRI should be the study of choice. MRIs performed with the patient seated upright (vs. laying supine) are not better for diagnosing CSF leaks, but are more than twice as effective at diagnosing cerebellar tonsillar ectopia, also known as Chiari malformation. Cerebellar tonsillar ectopia shares many of the same symptoms as CSF leak, but originates either congenitally or from trauma, including whiplash strain to the dura.

An alternate method of locating the site of a CSF leak is to use heavily T2-weighted MR myelography. This has been effective in identifying the sites of a CSF leak without the need for a CT scan, lumbar puncture, and contrast and at locating fluid collections such as CSF pooling. Another highly successful method of locating a CSF leak is intrathecal contrast and MR Myelography.

The most common missed lesion is within the nasal cavity, where a fibrosed nasal polyp may be considered. However, it does not have glial tissue. Further, a polyp usually has mucoserous glands. The lesion is frequently misintrepreted as scar in the subcutaneous tissues, but scar in a <2 year old child would be uncommon. Special stains are frequently required to highlight the diagnosis.

When cranial CSF leak is suspected because of discharge from the nose or ear that is potentially CSF, the fluid can be collected and tested with a beta-2 transferrin assay. This test can positively identify if the fluid is cerebrospinal fluid.

Colloid cysts can be diagnosed by symptoms presented. Additional testing will be required and the colloid cyst symptoms can resemble those of other diseases. MRI and CT scans are often used to confirm diagnosis.

Most arachnoid cysts are asymptomatic, and do not require treatment. Where complications are present, leaving arachnoid cysts untreated, may cause permanent severe neurological damage due to the progressive expansion of the cyst(s) or hemorrhage (bleeding). However, with treatment most individuals with symptomatic arachnoid cysts do well.

More specific prognoses are listed below:

- Patients with impaired preoperative cognition had postoperative improvement after surgical decompression of the cyst.

- Surgery can resolve psychiatric manifestations in selected cases.

Treatment focuses on monitoring and should be accomplished with inpatient floor service for individuals responsive to commands or neurological ICU observation for those with impaired levels of consciousness. Extra attention should be placed on intracranial pressure (ICP) monitoring via an intraventricular catheter and medications to maintain ICP, blood pressure, and coagulation. In more severe cases an external ventricular drain may be required to maintain ICP and evacuate the hemorrhage, and in extreme cases an open craniotomy may be required. In cases of unilateral IVH with small intraparenchymal hemorrhage the combined method of stereotaxy and open craniotomy has produced promising results.

A 2004 study suggested that the D-dimer blood test, already in use for the diagnosis of other forms of thrombosis, was abnormal (above 500 μg/l) in 34 out of 35 patients with cerebral sinus thrombosis, giving it a sensitivity of 97.1%, a negative predictive value of 99.6%, a specificity of 91.2%, and a positive predictive value of 55.7%. Furthermore, the level of the D-dimer correlated with the extent of the thrombosis. A subsequent study, however, showed that 10% of patients with confirmed thrombosis had a normal D-dimer, and in those who had presented with only a headache 26% had a normal D-dimer. The study concludes that D-dimer is not useful in the situations where it would make the most difference, namely in lower probability cases.

Diagnosis of IIA is based on finding an intracranial aneurysm on vascular imaging in the presence of predisposing infectious conditions. Positive bacterial cultures from blood or the infected aneurysm wall itself may confirm the diagnosis, however blood cultures are often negative. Other supporting findings include leukocytosis, an elevated erythrocyte sedimentation rate and elevated C-reactive protein in blood.

The most important initial investigation is computed tomography of the brain, which is very sensitive for subarachnoid hemorrhage. If this is normal, a lumbar puncture is performed, as a small proportion of SAH is missed on CT and can still be detected as xanthochromia.

If both investigations are normal, the specific description of the headache and the presence of other abnormalities may prompt further tests, usually involving magnetic resonance imaging (MRI). Magnetic resonance angiography (MRA) may be useful in identifying problems with the arteries (such as dissection), and magnetic resonance venography (MRV) identifies venous thrombosis. It is not usually necessary to proceed to cerebral angiography, a more precise but invasive investigation of the brain's blood vessels, if MRA and MRV are normal.

IIAs are uncommon, accounting for 2.6% to 6% of all intracranial aneurysms in autopsy studies.

Once suspected, intracranial aneurysms can be diagnosed radiologically using magnetic resonance or CT angiography. But these methods have limited sensitivity for diagnosis of small aneurysms, and often cannot be used to specifically distinguish them from infundibular dilations without performing a formal angiogram. The determination of whether an aneurysm is ruptured is critical to diagnosis. Lumbar puncture (LP) is the gold standard technique for determining aneurysm rupture (subarachnoid hemorrhage). Once an LP is performed, the CSF is evaluated for RBC count, and presence or absence of xanthochromia.